The present invention is generally directed to a system and method for providing percutaneous electrical nerve stimulation therapy. The present invention is more particularly directed to such a system and method capable of providing effective treatment to a large patient population automatically without requiring individual therapy tailoring or adjustment for each patient.
Electrical therapy has long been used in medicine to treat pain and other conditions. One such therapy is transcutaneous electrical nerve stimulation (TENS). This therapy involves the delivery of electrical energy through patch electrodes placed on the surface of a patient""s skin to treat pain in tissue beneath and around the location of the patch electrodes. The electrical energy is typically delivered to the patient in a waveform that varies according to a single preset frequency or to a limited frequency combination.
The relationship between waveform frequency and efficacy varies from patient to patient and from condition to condition. Prior art TENS studies therefore vary greatly in their conclusions regarding the efficacy of different TENS waveforms. For example, a review of 46 published TENS studies showed a wide variation in pain relief effect. It is difficult (if not impossible) to determine from these studies which waveform frequency should be used to treat a new patient or a prior patient with a new condition.
Some studies have attempted to determine the relationship between waveform frequency and the mechanism underlying the therapeutic effect, such as pain relief. For example, one study of 37 patients determined that TENS applied at a relatively low frequency (2 Hz) increased the concentration of an enkaphalin pain reliever in patients"" cerebral spinal fluid (CSF), while TENS applied at a relatively high frequency (100 Hz) increased the concentration of a dynorphin pain reliever in the CSF. These studies did not attempt to correlate the increased concentrations of these substances in the CSF with pain relief effect, nor did they suggest which patients would benefit more from one frequency or the other or which conditions were best treated at one frequency or the other.
Electrical therapy to treat pain and other conditions may also be delivered percutaneously. This percutaneous approach is commonly referred to as Percutaneous Neuromodulation Therapy (PNT) or Percutaneous Electrical Nerve Stimulation (PENS). Like the TENS studies, however, published studies describing percutaneous electrical therapy have focused on limited patient populations and on limited frequencies and frequency combinations. These studies do not guide clinicians in the treatment of any particular patient with unknown electrical therapy response characteristics and an unknown condition underlying the apparent symptoms.
Thus, a significant drawback of prior art electrical therapy approaches is their failure to provide a therapeutic regime that will be efficacious across entire populations of patients and across a variety of patient conditions. At best, prior art approaches require trial and error testing of the patient to determine which waveform frequency would be best to treat that patient""s condition, thereby consuming scarce medical personnel time and delaying the possible therapeutic effect for the patient. At worst, the prior art electrical therapy systems take a xe2x80x9cone size fits allxe2x80x9d treatment approach with widely varying results.
It is therefore an object of this invention to provide an electrical therapy system and method that maximizes efficacy across patient populations and patient conditions.
The present invention therefore provides a method of providing percutaneous electrical therapy to a patient, which renders the therapy effective for a large patient population and a broad range of patient conditions. The method includes the steps of inserting an electrode into the patient and applying an electrical signal between the electrode and the patient""s body at a plurality of frequencies that automatically vary over a range having a minimum frequency of at most about 20 Hz and having a maximum frequency of at least about 40 Hz.
The electrical signal preferably includes a plurality of pulses with each consecutive pair of pulses being separated by an interpulse interval. The interpulse intervals may be automatically varied monotonically or randomly.
The method may further include the step of compensating the electrical signal for changes in frequency of the electrical signal. The compensation may be in the form of amplitude or pulse width adjustments to provide effective signal energy over the range of frequencies.
The present invention further provides a system for providing percutaneous electrical therapy to a patient. The system includes electrode means insertable into the patient and signal generating means for applying an electrical signal between the electrode means and the patient""s body, the signal generating means including frequency varying means for applying the electrical signal between the electrode means and the patient""s body at a plurality of frequencies that automatically vary over a range having a minimum frequency of at most about 20 Hz and having a maximum frequency of at least about 40 Hz.
The electrical signal preferably includes a plurality of biphasic pulses, each biphasic pulse including a consecutive pair of pulses, and each consecutive pair of biphasic pulses being separated by an interpulse interval. The frequency varying means may vary the interpulse intervals monotonically or randomly to automatically vary the frequency of the electrical signal.
The system may further include compensating means for compensating the electrical signal for changes in frequency of the electrical signal. The compensation may adjust amplitude or pulse width of the electrical signal to provide signal energy over the frequency range.
The present invention still further provides a system for providing percutaneous electrical therapy to a patient comprising at least one electrode insertable into the patient and a signal generator adapted to be coupled between the at least one electrode and the patient""s body. The signal generator provides an electrical signal at a plurality of frequencies that automatically vary over a range having a minimum frequency of at most about 20 Hz and having a maximum frequency of at least about 40 Hz.